1. Field of the Invention
The present invention relates to a semiconductor technology process for producing a conductive layer.
2. Description of the Related Art
Although the present invention is described in connection with the fabrication of capacitors in semiconductor substrates, the invention is not restricted to this particular application, but rather relates in general terms to the production of thin conductive layers.
For reasons which are generally known, in semiconductor technology it is preferred to use processes which allow the highest possible integration density of semiconductor components. Capacitors represent one example of semiconductor components which are very frequently required, in particular for semiconductor memory components. To fabricate capacitors, trenches with a high aspect ratio are typically etched into a semiconductor substrate, and a first electrode, an insulation layer and a second electrode are successively deposited on the trench base and the trench side walls. The typical capacitor shapes are named according to the sequence of the individual layers deposited in the trenches and include, for example, an MIM (metal insulator metal) capacitor or an MIS (metal insulator semiconductor) capacitor. The capacitance of the capacitor is proportional to the surface area of the insulation layer. To enable the capacitance to be as high as possible, the first electrode must be as thin as possible in the trench, in particular in the region of the trench base. One known material for the first electrode is titanium nitride. Titanium nitride has a tendency to grow at the trench base with a vertical grain structure. The typical size of these grain structures is about 5 nm. Layers which are of the same thickness as the size of the grain structures have grain boundaries which run from an upper surface to a lower surface of the layer. Impurities can diffuse along these grain boundaries during the semiconductor fabrication process. Typical impurities include chlorine or oxygen. These impurities lead to intermediate states in the semiconductor substrate. These intermediate states localize charge carriers and in this way lead to parasitic capacitances. Since these parasitic capacitances need to be avoided, the diffusion has to be suppressed, and therefore the minimum layer thickness of the titanium nitride has to be selected to be significantly larger than the grain structure of titanium nitride, i.e. 5 nm.
As described above, further layers are then deposited on the titanium nitride layer. It is found in this context that the quality of the layers subsequently deposited depends to a considerable extent on the roughness of the surface of the titanium nitride layer. Thin titanium nitride layers give rise to a mean roughness of about 1 nm, on account of the grain structure. The result of this is that further layers are deposited on a thin titanium nitride layer of low quality, or a high level of outlay is required for the deposition of these layers.